Heavy metal bearing paint residue, and mixtures of heavy metal bearing paint residue and spent paint removal blasting or abrasive media, may be deemed “Hazardous Waste” by the United States Environmental Protection Agency (USEPA) pursuant to 40 C.F.R. Part 261 and also deemed hazardous under similar regulations in other countries such as Japan, Switzerland, Germany, United Kingdom, Mexico, Australia, Canada, Taiwan, European Countries, India, and China, and deemed special waste within specific regions or states within those countries, if containing hazardous waste regulatory method extraction fluid solution-soluble and/or sub-micron filter-passing particle sized heavy metals such as; Arsenic (As), Silver (Ag), Barium (Ba), Lead (Pb), Cadmium (Cd), Chromium (Cr), Mercury (Hg), Selenium (Se), Copper (Cu), Zinc (Zn), and Antimony (Sb), above levels deemed hazardous by those country, regional and/or state regulators.
There exists a need for methods that reduce the solubility of mixed heavy metal bearing paint residue and spent blast media, such that the extract from these mixtures contains minimal concentrations of heavy metals that fall within limits deemed allowable by the U.S. and other countries, enabling such mixtures to be classified as non-hazardous waste.
The prior art has focused on reducing solubility of heavy metals, mostly lead, from paint residues by application of phosphate sources blended with Latex and silicates onto surfaces prior to blasting (Forrester U.S. Pat. No. 6,515,053 B1), application of certain acidulated calcium phosphates such as triple superphosphate and diammonium phosphate blended with blast media used for painted surface removal by air blasting (Forrester U.S. Pat. No. 6,186,939 B1), and post-paint removal blasting application of known heavy metal stabilizers such as phosphates, carbonates, cement, silicates, with or without mineral complexers, in accumulation tanks or waste piles after collection or accumulation of the paint residue (Forrester U.S. Pat. No. 5,846,178, Forrester U.S. Pat. No. 5,722,928 and Forrester U.S. Pat. No. 5,536,899 and references cited therein).
Several other methods have been investigated to decrease the amount of heavy metal in industrial wastes. U.S. Pat. No. 5,202,033 describes an in-situ method for decreasing Pb Toxicity Characteristic Leaching Procedure (TCLP) leaching from solid waste using a combination of solid waste additives and additional pH controlling agents from the source of phosphate, carbonate, and sulfates. U.S. Pat. No. 5,037,479 discloses a method for treating highly hazardous waste containing unacceptable levels of TCLP Pb such as lead by mixing the solid waste with a buffering agent selected from the group consisting of magnesium oxide, magnesium hydroxide, reactive calcium carbonates and reactive magnesium carbonates with an additional agent which is either an acid or salt containing an anion from the group consisting of Triple Superphosphate (TSP), ammonium phosphate, diammonium phosphate, phosphoric acid, boric acid and metallic iron. U.S. Pat. No. 4,889,640 discloses a method and mixture from treating TCLP hazardous lead by mixing the solid waste with an agent selected from the group consisting of reactive calcium carbonate, reactive magnesium carbonate and reactive calcium magnesium carbonate. U.S. Pat. No. 4,652,381 discloses a process for treating industrial wastewater contaminated with battery plant waste, such as sulfuric acid and heavy metals by treating the waste waster with calcium carbonate, calcium sulfate, calcium hydroxide to complete a separation of the heavy metals. Recently, calcium phosphates have been investigated (Forrester US 2012/0220810).